Cytoplasmic incompatibility for the control of eradication of Culex pipiens and Aedes polynesiensis is being studied. The relationship of symbiont infections to incompability and to female meiosis is being studied. Symbionts will be characterized morphologically, attempts will be made to grow them in vitro, and they will be sought in other species of mosquitoes. A release strain which produces few females is under development. Formal genetic studies of these species are being carried out to produce new tools for studying genetic control; the inheritance of esterases is currently under study. The dynamics of a field population subjected to genetic control will be studied if the opportunity presents itself.